British Geological Survey

TECHNICAL REPORT WC/95/2 Overseas Geology Series

Project Summary Report. Environmental impact of gold and complex sulphide mining (with particular reference to arsenic contamination)

T M Williams and N Breward Minerals and Geochemical Surveys Division

A report prepared for the Overseas Development Administration under the ODA/BGS Technology Development and Research Programme, Project 9U6.

ODA classification

Subsector: Geoscience

T h e t ~ : G2 Identify and ameliorate minerals-~lated and other geochemical toxic hazards

Project title: Envinwrmental Impact of Gold and Complex Sulphide Mining

Project Reference: R5553

Bibliographic reference: Williams T M & Breward N Environmental impact of gold and complex sulphide mining (with @cuk reference to arsenic contamination).

Key words: Mining, gold, complex sulphides, arsenic, geochemistry, ecotoxicology, mine drainage, Zimbabwe, Malaysia, Philippines, Thailand.

Cover illustration: Tailings impoundment, Globe and Phoenix mine, Zimbabwe.

EXECUTIVE SUMMARY

An investigation of the geochemical toxic hazards associated with gold and complex sulphide mining in tropical regions, with particular reference to arsenic and heavy metals, was undertaken by the British Geological Survey (BGS) as a component of the Overseas Development Administration (ODA) Technology Development and Research (TDR) Programme during the period April 1992 - March 1995. Collaborative support in specific mineralogical and ecotoxicological aspects of the study was provided by the (British) Natural History Museum and the Institute of Terrestrial Ecology. A synopsis of the principal activities and findings of the project, drawn from site-specific information presented in ten ODA-BGS technical reports, is provided in this volume.

Precious and base-metal mining and refining is of fundamental economic importance in many developing countries, yet the environmental cost of ill-managed deposit exploitation can be severe. Environmental hazards are often most pronounced in tropical regions, where high rates of chemical weathering and biochemical activity induce the rapid mobilisation of potentially toxic elements from mine-waste. Governments throughout the developing world now recognise the need to formulate environmental policy and controls for the mining and mineral processing sector. However, legislation can be difficult to enforce (and it's success hard to evaluate) in the absence of appropriate monitoring and pollution mitigation strategies.

The fundamental objectives of the study, as defined at the outset of the research, were:-

(i) characterisation of the processes controlling arsenic and toxic heavy metal mobil- isation and transport in gold and complex sulphide mining localities. (ii) development and field validation of methods for monitoring contaminant levels and their ecotoxicological or human impact. (iii) formulation of practical, cost-effective remediation strategies for minimising contaminant impacts in tropical developing regions. (iv) evaluation of the role of geological setting, ore mineralogy and mining technol- ogy as determinants of mine drainage chemistry, with a view to the development of a predictive model.

Some 50 field sites in Malaysia, the Philippines, Thailand and Zimbabwe, encompassing a diverse range of climatic, geological and technological settings, were selected for study, in close liaison with government and private sector institutions in each country. A standardised methodology was applied at each locality (subject to physiographic constraints) to ensure maximum inter-site data comparability. The methodology was designed to facilitate:- (i) characterisation and hazard assessment of As and heavy metal contaminant sources, (ii) monitoring of the extent and pathways of As and heavy metal dispersal in water, soil and sediment, (iii) assessment of toxic trace element bioassimilation by aquatic and temstrial biota and (iv) assessment of ecotoxicological impacts.

Mineralogical studies (incorporating conventional and newly developed techniques) have confirmed the considerable potential of 'environmental mineralogy' as a tool for assessing the toxic hazard posed by mine waste. The rate of As and toxic metal release from tailings or waste rock accumulations has been found to be (indirectly) related to the rate at which sulphide minerals are oxidised. Although partially controlled by inherent variations of sulphide resistance, this rate can be regulated by careful management of the permeability and redox characteristics of the waste pile. The relationship between sulphide oxidation rate and Adheavy metal liberation into surface or groundwaters is, however, complicated by the interim formation of secondary mineral phases, the solubility of which can vary considerably. With respect to As, the formation of the secondary arsenate mineral scorodite (following the weathering of sulphides such as arsenopyrite) has been found to exert a marked constraint on the aqueous release of As from sulphide-rich waste. Regulation of the internal characteristics of waste piles (including pWEh regime and iron content) can be

instrumental in promoting the formation of this phase, rather than more soluble Ca- arsenates; sulpharsenates and oxides.

Hydrochemical investigations have confirmed the presence of As in many tropical mine- waters at concentrations which exceed the WHO potable water threshold (10 pg/l) by up to a factor of 720. Acute enrichment has been reported for waters of widely varying pH (0.6 - 9.9, indicating that As mobilisation is not, as commonly perceived, a hazard exclusively associated with acid mine drainage (AMD).

The multi-element composition of mine-waters, although influenced by external factors such as climate and mining technology, has been found to be predominantly controlled by inherent geochemical and geological site variables. Predictive modelling of the chemistry of mine drainage (with respect to pH and trace element content) at individual sites is quite plausible, provided that input data for the critical 'first order' controls can be provided (or estimated). A basic model framework, involving simple geological and geochemical input parameters and a combined thermodynamic/sorption modelling code, has been established with a view to future use for environmental impact assessment.

The mechanisms of As and heavy metal transport (and deposition) in mine drainage are non-uniform. Accurate characterisation of the processes operating at any given site is a vital prerequisite for the design of an appropriate pollution mitigation strategy. At the study sites investigated, four Adheavy metal transport and attenuation systems were commonly encountered:-

(i) systems in which contaminant solubility is directly related to saturation with respect to ferric oxides. (ii) systems in which contaminant mobility is related to iron-sulphate solubility. (iii) systems in which As mobility is controlled by redox conditions. (iv) systems in which complexing agents such as cyanide compounds control contaminant mobility.

The formation of hydrous ferric oxide 'ochres' in mine-water drainage systems can be unsightly and frequently results in localised biological degradation. The process does, however, provide a highly effective matrix for the scavenging of toxic elements (including As) from solution. In contrast to most sulphate precipitates, the common hydrous ferric oxide minerals (e.g. limonite, ferrihydrite and goethite) are also relatively insoluble, and can hence be considered to form long-term sinks for toxic elements. The precipitation of such oxides can, therefore, potentially be harnessed as a component of low-cost waste- wa&r decontamination strategies for tropical gold and complex sulphide mining localities.

Buffering methods entailing the addition of lime or emplacement of limestone drains have conventionally been used to precipitate toxic trace elements from acid mine-waters. Data collected during this study have, however, shown that such methods can be inadequate for the removal of As, due to its high solubility across a wide pH range. The utility of a range of alternative remediation options for As-contaminated mine sites in tropical environments was examined on the basis of three criteria: (i) the cost and availability of the resources required for implementation (ii) the extent and cost of post-implementation maintenance and (iii) method versatility. Wetland systems, which act to remove toxic elements from mine- waters by particulate sedimentation, sulphide precipitation, hydrous oxide formation, organo-metallic complexation and cation-exchange processes, have shown considerable potential at sites in southern Africa and Asia. The applicability of wetlands is, however, limited in steep, deeply incised valleys, such as prevail in much of East Malaysia and the Philippines-The potential and efficiency of induced ferric oxide precipitation for scavenging heavy metals and arsenic from mine-waters at a Cu-Au mining operation in Sabah, East Malaysia, was investigated using a combination of empirical (sequential extractive speciation) and simulative (saturation-speciation and sorption modelling) methods.

Hydrochemical processes in mine-waters can be characterised using simulative geochemical modelling. The potential of the code WATEQ4F for this purpose has been assessed throughout the project, and successfully applied for predicting the extent of As and heavy metal dispersal at several sites. The model has also been used to determine the likely hazard potential of elements such as As, the toxicity of which is markedly influenced by aqueous speciation. Problems with the approach have, however, been encountered, notably due to failure of thermodynamic models to account for kinetic factors in mine-water hydrogeochemical reactions. Difficulties have also been evident when modelling speciation in very high ionic strength solutions.

,

Comparative studies of soil As enrichment in areas of (i) pristine mineralisation and (ii) acute mining disturbance have provided strong evidence that post-mining concentrations are accentuated due to increased rates of physical and chemical mobilisation from mine waste. In most circumstances the bioavailability of As in tropical soils is low, due to the scavengingbinding effects of ferric oxides in the regolith. However, considerable As mobility and attendant plant uptake has been noted in certain iron-poor alluvial soils.

The uptake of As and heavy metals by aquatic and terrestrial biota around gold and complex sulphide mining operations was investigated at selected sites in Malaysia and Zimbabwe. Preliminary results for As in filamentous algae from flooded alluvial gold workings showed evidence of acute accumulation (up to 7000 pg/g).The concentrations reported for fish muscle samples from the same localities were, however, surprisingly low ( ~ 0 . 2 pg/g). Terrestrial vegetation, including agricultural crops such as maize, showed evidence of As accumulation to hazardous concentrations (> 10 pg/g) exclusively within areas of Zimbabwe with low soil iron and phosphate content (4% and <0.1% respectively).

The development of a simple, cost-effective technique for assessing ecotoxicological stress induced by mining-related As and heavy metal contamination in tropical environments was identified as a major priority at the project outset. A pioneering biomarker method has been developed, involving the extraction of coelomic fluid from invertebrate samples using an ultrafine hypodermic needle, and staining of the fluid cells with neutral-red dye. Because the ability of the cells to uptake and retain the dye in the lysosomal compartment is directly related to cell health, observation of the rate of dye leakage (using an optical microscope) can provide an immediate indication of cell dysfunction. The technique was successfully tested along a known soil-As concentration gradient near the Wanderer gold mine in Zimbabwe, where dye retention times showed a clear increase with increasing distance from the contaminant source. The success of this simple method may have important implications for the future design of environmental monitoring programmes for mining localities worldwide.

The research conducted under BGYODA TDR programme 92/6 (ref. 5553) has provided a basic framework for monitoring, predicting and mitigating mining-related As and heavy metal contaminant hazards in tropical developing regions. However, the extent of practical 'take-up' of research findings in SE Asia and southern Africa has, to date, been widely variable. Such variations serve to emphasise the need to complement international technical support, of the nature provided by the ODA, with domestic legislative pressure to promote (or enforce) environmental protection.

CONTENTS

1:

2:

3:

4:

5:

6:

7:

8:

9:

A l :

A2:

INTRODUCTION

BACKGROUND

STUDY OBJECTIVES

COLLABORATIVE FRAMEWORK 4.1: UK Collaboration 4.2: Overseas collaboration

PROJECT DESIGN

RESULTS 6.1: Site monitoring

6.1.1: Contaminant sources: 6.1.2: Hydrochemical monitoring: 6.1.3: Contaminant transport 6.1.4: Geochemical modelling 6.1.5: Soil studies 6.1.6: Bioassimilation studies 6.1.7: Ecotoxicological monitoring

6.2: Hazard mitigation and remediation 6.3: Predictive modelling

RESEARCH TAKE-UP

CONCLUSIONS

ACKNOWLEDGEMENTS:

APPENDIX 1: PROJECT TECHNICAL REPORTS

APPENDIX 2: OTHER PUBLICATIONS/PRESENTATIONS

3

5

3 6 3 9

4 1

4 2

4 3

4 4

4 5

A3: APPENDIX 3: LOCAL DISSEMINATION 4 6

1: INTRODUCTION:

This report summarises the objectives, results and developmental implications of a study of the environmental impacts of gold and complex sulphide mining in tropical regions, with particular reference to the mobilisation of arsenic and other potentially toxic trace elements by extractive and related mineral processing activities. The research was carried out during the period April 1992 - March 1995 as a component of the Overseas Development Administration (ODA)/British Geological Survey (BGS) Technology Development and Research (TDR) programme (project reference 5553,92/6). The programme forms part of the British Government's provision of aid to developing countries.

This document aims to convey the salient findings of the study in a manner which may assist government and development agency personnel from a variety of disciplinary backgrounds including scientists, planners and engineers. Such a format is consistent with the BGSIODA desire for wider dissemination of TDR research findings. Detailed information regarding specific technical aspects of the project is provided in a series of BGS-ODA technical reports describing case-studies in Zimbabwe, east and west Malaysia, the Philippines and Thailand (detailed in Appendix 1). Due to the sensitive nature of the hydrogeochemical and ecotoxicological data collated for certain study sites, several technical reports have necessarily been assigned a 'restricted' BGS/ODA classification.

2: BACKGROUND:

The metalliferous minerals sector is of considerable economic importance to numerous nations worldwide. However, the requirement for mining operators to minimise the adverse environmental impacts of gold and base-metal exploitation is increasingly being recognised (by both government regulatory authorities and by the mining industry itself). The geochemical hazards associated with metalliferous mining can be particularly severe in tropical countries, where high rates of chemical weathering and biogeochemical cycling induce rapid mobilisation of toxic elements from mine-waste. In less developed regions, such environmental problems may be further accentuated by a lack of legislative control on the mining sector, or by logistic difficulties of policy enforcement.

The ecotoxicological and human health effects of arsenic (As), a contaminant commonly associated with gold mining activities, have been subject to increasing concern in recent years. Arsenic is enriched (principally as arsenopyrite) in auriferous sulphide assemblages in many of the world's classic gold-producing regions, and is routinely used in exploration as a gold 'pathfinder'. Following mining and the exposure of arsenic-bearing sulphides to the atmosphere, As may be rapidly mobilised into surface drainage and groundwaters. The

1

potential human effects of prolonged exposure to As are well documented and incrude the skin diseases hyperkeratosis, hyperpigmentalion, malignant melanoma; peripheral arterio- sclerosis (Black foot disease), bladder, liver and kidney cancers. However, the true impact of mining-related As contamination on aquatic ecosystems and human water or food resources in most tropical gold mining provinces remains to be fully appraised.

Mining of complex sulphides generates sub-ore grade waste which, on weathering. can liberate a range of toxic trace elements (including As, Sb. Bi, Pb, Zn, Cu, Cd, CO and Ni). The simultaneous generation of a strongly acid drainage regime (through sulphide oxidation mechanisms described in project technical reports WC/94/9/R and WC/94/65/R) also serves to enhance metal solubility and dispersal in sur4ace drainage and groundwaters. In Europe and North America. the requirement for mining operators to minimise the impact of metal- rich drainage from polymetallic waste is explicitly embodied within mining legislation, and a substantial environmental/geotechnical consultancy sector has grown to provide technological expertise for waste-water treatment and site remediation. Much of the R&D undertaken in this sector has. however, focused on the formulation of high-technology (high- cost) methods, suitable for large scale-mining operations in temperate regimes. Considerable modification of existing engineering and (bio)chemical pollution control technologies is required in order to meet the socio-economic, climatic and physiological requirements of tropical developing regions.

3: STUDY OBJECTIVES:

Following the establishment of appropriate collaborative links, field evaluations of the

geochemical impacts of gold and complex sulphide mining were conducted in Zimbabwe, Malaysia, the Philippines and Thailand. These countries provided an ideal range of climatic and geologicaYmetallogenic conditions under which to fulfil1 the principal objectives of the study:-

(i) to characterise the processes controlling arsenic and toxic heavy metal mobilisation, transport and attenuation in the vicinity of gold and complex sulphide mining activities.

( i i ) to develop and test methodologies for monitoring contaminant levels, their ecotoxicoiogical impact and human hazard potential in tropical regimes (suitable for long term utilisation by government departments and legislative agencies).

( i i i ) to formulate practical, cost-effective remediation strategies for minimising contaminant impacts in tropical developing regions.

2

(iv) to establish the role of geological setting, ore mineralogy and mininglprocessing technology as determinants of drainage geochemistry and contaminant mobilisation for predictive/modelling purposes.

4: COLLABORATIVE FRAMEWORK

4.1 UK collaboration: All aspects of the project research were coordinated and led by BGS. Specialist support for ecotoxicological impact assessment studies in Malaysia and Zimbabwe was provided through collaboration with the Institute of Terrestrial Ecology. A modest input to biological and mineralogical field studies in Malaysia was provided by staff of the NHM.

4.2: Overseas collaboration: In each study region, a collaborative framework was established incorporating relevant government authorities, particularly those institutions with responsibility for mineral licensing and environmental issues. Liaison with commercial sector mining companies was also considered important. In many developing countries, improved self-regulation by the minerals sector may ultimately be more effective than environmental legislation due to the lack of resources for routine monitoring and legal enforcement by government departments. An insight into commercial sector operating costs in developing countries was also considered desirable, to ensure that technical recommendations for site remediation could be balanced against economic viability. A summary of the principal overseas collaborators involved in the project is provided in Table 1.

5: PROJECT DESIGN

The project was conceptually designed to incorporate four discrete phases (Fig. l), each requiring its own methodology:-

Phase 1: Monitoring systems: For all sites, a phase of empirical monitoring was considered vital to provide fundamental data showing the magnitude and composition of mining-derived contaminant fluxes, the extent of dispersal and the likely human or toxicological impacts.

Phase 2: Understanding systems: An understanding of the natural hydrochemical, sedimentary and pedological processes which regulate the transport and deposition of toxic elements (within any given geological, climatic and technological setting) is an important pre-requisite for successful mine-site remediation system design. A research phase aimed specifically at characterising such processes, and assessing the potential for human modification, was thus considered important.

3

a w ct

s U w +

* CL c z 3 C U

0 n .- e

4

Figure 1: Environmental impact of gold and complex sulphide mining: Conceptual project design

PHASE 1: PHASE 2: ~ MONITORING SYSTEMS SYSTEMS 1 \ /) \ /

PROJECT

MODIFYING SYSTEMS (inc. remediation)

DESIGN

PHASE 4 PREDICTING SYSTEMS

(modelling)

Phase 3: Modifying systems: Output from phases 1-2 was intended to provide a sound basis for assessing the need for pollution mitigation at individual study sites, and for evaluating the merits of alternative technical approaches to ameliorating contaminant hazards. A 'solution design' phase, with emphasis on the development of long-term remediation schemes which work with, rather than against, natural processes of contaminant immobilisation, was thus planned to follow the completion of the 'monitoring' and 'characterisation' phases at selected sites.

Phase 4: Predicting systems: At the prqject outset, it was postulated that an empirical database, showing the manner in which geological, technological and climatic factors interact to control the magnitude and composition of mine-derived contamination, could be used to develop a predictive model for assessing likely post-mining contaminant fluxes from hitherto unexploited mineral deposits. An effort was made throughout the project to select field sites with widely variable geological, metallogenic, physiographic and climatic characteristics, in order to make the database as representative as possible. The range of deposits visited (Table 1) included numerous mesothermal and epithermal vein systems, polymetallic skarns, Cu-Au porphyries, stratabound disseminated gold and alluviaVplacer deposits.

6: RESULTS

6.1: Site monitoring Field investigations in the vicinity of some 50 gold and base-metal mining operations were carried out by BGS geochemists during September 1992 (Peninsular Malaysia), March 1993 (Zimbabwe), August 1993 (Sabah and Sarawak), February 1994 (Zimbabwe), May 1994 (Sabah and the Philippines) and August 1994 (Thailand). An ITE ecotoxicologist was present

5

during visits to Malaysia in 1992 and Zimbabwe in 1994. An additional independent visit to Malaysia was made by a mineralogist and a life scientist from the NHM in February 1994.

A standardised sampling and monitoring methodology was formulated for use at all study sites (subject to physiographic constraints) to ensure the development of a coherent database, with a high degree of between-site data comparability. For each site, the methodology was intended to satisfy the following criteria:-

1: characterisation and hazard assessment of As and heavy metal contaminant sources. 2: monitoring of the extent and pathways of As and toxic heavy metal dispersal in water. 3: monitoring of As and toxic heavy metal dispersal in soil and sediment. 4: assessment of toxic trace element bioassimilation (by aquatic and terrestrial biota). 5: assessment of ecotoxicological impacts.

A multi-media approach, involving established BGS sampling/analytical methods for mine- waste, surface waters, soil, drainage sediment, and aquatic/terrestrial biota (including agricultural crops where appropriate) was adopted for routine data collection (outlined in detail in technical reports WC/94/20/R, WC/94/09/R and WC/94/65/R). The need to develop new methods, specifically tailored for contaminant source, transport and fate appraisal in tropical developing countries was also recognised and addressed.

6.1.1 : Contaminant sources: Exposed orebodies (in adits or open pits, Figs 2-3), waste-rock piles (Fig. 4), tailings accumulations (Figs. 5-6) and impoundments holding residueshluids derived from recovery processes such as flotation or cyanidation (Fig. 7) can all constitute 'reservoirs' for toxic trace metals in areas of gold and base metal mining. At any given site, the characterisation of such contaminant sources with respect to total toxic element content, composition and weathering rate (i.e. rate of contaminant release) can provide a valuable insight into the nature and magnitude of the potential environmental hazard.

Compositional and mineralogical studies of mine waste from study localities in Malaysia, Zimbabwe and Thailand were undertaken, using conventional techniques of ore mineral characterisation (including SEWlight microscopy, electron microprobe analysis, X-ray diffraction, IR spectroscopy) to establish the factors controlling the environmental release of As and other potentially toxic elements from such material. The principal observations can be summarised as follows:-

6

1: At the majority of field sites, sulphide minerals formed the main carriers of toxic trace elements. The rate of sulphide oxidation following exposure to surface environment conditions (for example in waste rock or tailings piles) thus emerged as a critical determinant of contaminant mobilisation rates. The mechanics of sulphide weathering processes in tropical regimes were investigated in detail by the NHM (Bowell, 1994) and the universally operative chemical processes are summarised in technical reports WC/94/09/R, WC/94/65/R and WC/94/78R.

2: Sulphide oxidation rates, and hence toxic trace element release rates, were found to vary markedly between field sites. This, in part, reilects 'external' controls such as ambient temperature, humidity, pWEh regime and water-rock interaction (permeability). In waste- rock or tailings environments, such variables can to some extent be regulated. An understanding of their interaction is thus directly relevant to the prediction and management of geochemical hazards. During the present study, an example was encountered at the Globe and Phoenix mine, Zimbabwe, where a technique for tailings stabilisation involving the deposition of soil horizons (1 -2 m thick) between successive layers of tailings also serves to reduce water percolation, and hence sulphide oxidation, in the deeply buried/basal layers of the tailings pile.

3: In addition to external controls, micro-mineralogical data for sample assemblages containing a range of sulphides have shown that individual sulphide species possess inherently variable resistance to oxidation (Fig. 8). A decrease in degradation rate was typically observed through the sequence pyrrhotite > chalcocite > galena > sphalerite > pyrite > enargite > marcasite > chalcopyrite > molybdenite. In all cases, oxidation appeared most rapid in mine waste holding sulphides as fine-grained framboidal or poorly crystalline particles. Pyrite and other sulphides appeared increasingly prone to oxidation where high trace element impurities were present. These observations have important implications for future EIA studies of tropical mining localities, as characterisation of the sulphide mineralogy of waste can provide a rapid indication of the nature and magnitude of toxic metal fluxes which may be released.

4: Following the oxidation of primary sulphides, the mobility of As and heavy metals in mine waste at many sites was found to be restricted by the precipitation of secondary minerals or alteration coatings on sulphide surfaces. The chemistry, mineralogy, stability and solubility of these secondary phases is critical to the rate of toxic trace element release into surface drainage and groundwaters. Research into the environmental properties of secondary minerals of heavy metals such as lead has been in progress for over a decade. However, little is known of the physico-chemical characteristics of weathering products derived from the weathering of primary As minerals. In the case of lead, mobilisation from galena (PbS)-rich mine waste

10

or soil is often impeded by 'armouring' or 'encapsulation' of the sulphide grains with insoluble coatings of secondary minerals such as cerussite (PbC03) and pyromorphite (Pb4(PbCl)(P04)3). Conversely, the formation of soluble lead oxides on galena grain surfaces can result in problematic levels of mobile , bioavailable lead. In the present study. considerable emphasis was placed on determining whether or not similar variations occur in the behaviour of secondary As minerals.

Figure 8: Sulphide resistance to oxidation: mineralogical, granulon~etric and morphological controls.

MINERALOGY

PYRRHOTITE CHALCOCITE GALENA SPHALERITE PYRITE ENARGITE MARCASITE CHALCOPYRITE MO LY B DENITE

GRAIN SIZE TEXTURE TRACE ELEMENTS

I FINE FRAMBOIDAL HIGH COLLOFORM

MEDIUM

COARSE EUHEDRAL LOW INCREASED RESISTANCE

Data obtained from electron microprobe investigations of mine waste from several sites in Malaysia, Zimbabwe and Thailand suggest that the paragenetic sequence (i.e. the sequence of secondary mineral formation and alteration) which follows the breakdown of primary As assemblages is more complex than previously envisaged. The most common (and simplistic) process involves the oxidation of arsenopyrite (FeAsS) and in-situ formation of scorodite (FeAs04.2H20) or similar ferric arsenates. This process, widely observed in adits at Penjom, Peninsular Malaysia (technical report WC/94/20/R), tailings at Globe and Phoenix, Zimbabwe (technical report WC/94/65/R) and Ron Phibun, southern Thailand (technical report WC/94/79/R), produces a relatively insoluble weathering product, and hence slow rate of As release into aquatic systems. However, in instances where complex primary As assemblages (including native arsenic, arsenopyrite and realgar) were encountered in mine waste (as in the Bau area of Sarawak, Figs. 9- 10, technical report WC/94/67/R) the alteration products included higher-solubility phases such as arsenolite (AszO3). orpiment, pitticite (Fe arsenate/sulphate) and a range of As-bearing jarosites (complex sulphates). The partitioning of As between these secondary minerals is apparently controlled by subtle variations in ambient pH, Eh and the availability of reactants such as iron and sulphur. By improving our

1 1

understanding of these controls, it should be possible to model or predict the conditions under which high rates of As mobilisation may occur and to modify waste-pile environments accordingly. For example, problems of As-rich discharge (1-15 mg/l) from mine waste noted during the present study (e.g. Globe and Phoenix, Zimbabwe) have routinely been found to occur where waste or overburden holds a low (4%) total iron concentration. Supplementation with a suitable Fe-oxide compound could thus form a valuable part of future amelioration management strategies.

5 : The BGS has developed a rapid, low-cost methodology for appraising the granulometric and mineralogical partitioning of As and heavy metals in tailings and mine-contaminated soil (detailed in technical report WC/94/50/R). The technique utilises equipment which is widely available in mine assay laboratories worldwide and can provide a rapid insight into the probable stability and long-term release rates of As and toxic metals in waste piles at any given site. The method entails the analysis of size-fractioned and gravimetrically-separated components of waste in such a manner that the Adheavy metal fractions within primary sulphides, detrital gangue minerals, clays and secondary precipitates can be isolated. Most importantly, the proportion of potentially toxic elements present in volatile or easily leached phases can also be determined.

Examples of output data derived from the technique are provided in Tables 2 and 3. Table 2, showing the particle size and associated As distribution of tailings from Ron Phibun, Thailand, illustrates a number of characteristics common to waste samples from virtually all study sites. A bimodal particle size distribution is apparent, dominated by coarse (>1 mm) sandgravel fractions (in this case 390 g or 55% total mass), and an ultrafine (<20 pm) clay fraction (97g or 13% total mass). Weight-percentage data for the heavy mineral (HMC) and lighter 'tail' components in each of the sub-500 pm size fractions indicate that the HMC is only a small contributor to the total solid mass.

At virtually all study localities, As concentrations have been found to be highest in the fine (<63 pm) fractions of mine waste. The relative concentrations of As in the HMC and 'tail' components of this fine fraction can, however, vary widely. Table 2 illustrates a situation in which the fine (<125, <63, <20 pm) tail fractions of waste from Ron Phibun are both volumetrically dominant and hold high mass-specific As concentrations relative to the corresponding HMC fractions. This relatively unusual situation is symptomatic of particularly rapid or intense weathering and extensive alteration of (heavy) detrital sulphides (principally arsenopyrite) to lighter secondary arsenate minerals in the waste pile. More commonly, the HMC component of the finer particle size classes, while volumetiically small, holds high As concentrations relative to the lighter fraction, as exemplified by the selected data presented for tailings from Globe and Phoenix mine (Table 3).

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Table 2: Grain size and gravimetric partitioning of arsenic in Ron Phibun tailings sample RPT2.

Fraction Tot wt Tail wt % total HMC wt % total Tail A s As conc HMCAs

k) 9 ) @) t d % td

As conc.

%

>4mm

1-4mm

MSmm

216.6

174.2

61.5

>25@m

>125grn

>63pn

> 2 0 p

52.8 51.7 97.8 1.12 2.2 6.2

37.8 36.6 96.9 1.17 3.1 5.3

21.65 20.3 94.1 1.26 5.9 4.1

13.3 12.5 93.7 0.83 6.3 3.6

Table 3: Grain size and gravimetric partitioning of arsenic in selected fractions of Globe and Phoenix tailings sample GPX 151.

11.9

14.4

18.9

28.7

28.8

3.7

0.12 10.7

0.10 8.5

0.10 7.9

0.07 8.4

<20grn

Evap.

6: Chemical analysis of the wash-water used during the sievinglsize fractioning of waste samples has proved invaluable for determining the abundance of toxic elements present in water-soluble forms (i.e.. the component which could be readily leached by percolating rain or drainage water in the field environment). Considerable between-site variations have been recorded, suggesting that the toxic geochemical hazard associated with waste accumulation, often of similar bulk geochemical composition, is non-uniform. At Ron Phibun (Table 2) and Globe and Phoenix (Table 3), water-soluble mineral phases were found to constitute up to 5% of the total tailings mass, yielding 3.7% and 193 pg/g As respectively. At other sites, including the Penjom mine area, Malaysia (technical report WC/94/20/R) and Wanderer mine, Zimbabwe (technical report WC/94/66/R), high concentrations of ferric oxide in the waste matrix were found to restrict the water-soluble As component to a few mg/l.

97.54 97.54 100 0 28.0

31.86 31.83 1 (HI 1.2

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Fraction Tot wt Tail wt 70 total HMC wt % total Tail As As conc. HMCAs As conc.

<63pm

4 0 p m

Evap.

18.87 18.66 >99 0.21 0.1 454 8400

14.00 14.00 100 2234 - 5.1 193

6.1.2: Hvdrochemical monitoring: At all study sites, hydrochemical surveys were undertaken to characterise the composition of water emanating from adits and waste dumps (the major contaminant sources), and to trace the extent of subsequent dispersal of As and heavy metals in the downstream drainage system. Established BGS sampling methods were supplemented by techniques for determining the chemical speciation of As and other redox-sensitive elements such as iron. Full details of the hydrochemical methodology are provided in each site report (most comprehensively in technical reports WC/94/65/R and WC/94/79/R).

An ARC-INFO-based GIS system (suitable for the presentation and interpretation of hydrochemical data for individual sites in conjunction with topographic, land use, hydrological and other relevant datasets) was established for use throughout the project. The requirement for rapid information exchange between UK and overseas collaborators was considered particularly important in the selection of a GIS framework, and an ARC-INFO system was considered most appropriate as it is increasingly being used by project counter- parts in SE Asia.

The hydrochemical database acquired for over 50 sites has confirmed thc markedly variable composition of drainage (Table 4), and has highlighted a number of recurrent trends which have a direct bearing on the future prediction and mitigation of mine-drainage hazards:-

1 : Contaminant hazards in mine-water systems are not, as commonly perceived, exclusively associated with the generation of acid mine drainage (AMD). Surface water pH conditions in potentially toxic mine-waters have been observed across the range 0.6-9.5. The former, recorded at Iron Duke mine near Mazowe, Zimbabwe (for details see technical report WC/94/78/R) is amongst the lowest pH values documented for mine-waters worldwide. Dissolved concentrations of Fe, Mn, Al, As, Cu and Zn (and Cr, CO, Ni, V) in this water were found to exceed international standards for potable waters by up to a factor of 1400 (see Table 5). Irrespective of toxic trace element content, such strongly acid conditions are (with the exception of a limited microbial population) incapable of sustaining biological activity. High pH waters (7.0-9.5) have, however, also been found to contain concentrations of As which exceed international potable watcr standards by a factor of >loo, with substantial enrichment of heavy metals such as Cu, Zn (Ni and CO) occasionally observed (for full details see technical report WC/94/65/R).

15

Table 4: Peak abundance of selected elements in (0.45 pm-filtered) drainage waters from mines in Zimbabwe, Philippines, Malaysia and Thailand (values given in mg/l; M = Malaysia, Z = Zimbabwe, T = Thailand, P = Philippines).

SITE I DH I .

~~

RonDhibun (T) 1 7.1 Dizon (P)

Philex (P)

Fe I Mn I A1

270 11.3 I - 494 I238 I1396 655 45 94

<1 <1 <1 <1 <I <1

132500 1211 12010

0.2 I 0.01 I 0.001

0.70 7132 7.4 12.8

3555421 72.0 I ND %--p+- 4698 0.03

c u

5 299 1.02

<0.01

34

20 0.001 98

25

Zn

<1 90 4.7

c0.01 29

55 0.008 7.2

4.2

TABLE 5: Selected threshold criteria for trace contaminants in (1) potable waters (CEC, US-EPA, WHO) and (2) for Protection of Fish and Aquatic Life (US-EPA 1986).

All element values are given in mgA.

Parameter 1 2

AI As Pb C r Cd c u Ni V Fe Mn Zn SO4

0.2 - 1.0 0.01 - 0.05 0.05 0.01 0.005 1 .0 0.05

1.0 0.5 5.0 250.0

-

- 0.40 0.004 - 0.50 0.004 - 0.40 0.05 - 0.10 0.001 - 1.0 0.05 - 0.25

0.01 - 5.0

2: The mobility and solubility of As can be maintained across a much wider pH range than most heavy metals (Fig 11). Numerous examples have been recorded of hazardous concentrations of As (>50 pg/l) in waters which arc neutral or mildly alkaline, and which exhibit very low heavy metal concentrations (for example Table 4: Lucky Hill, Ron Phibun). This has important implications for the design of pollution mitigation systems for As-

16

contaminated mine-waters, as conventional methods of AMD treatment, involving the precipitation of metals by buffering (i.e. reducing acidity ), may not effectively remove As.

Figure 11: Concentration trends of As and heavy metals (represented by Cu) in mine- waters at selected study localities, showing the general restriction of heavy metal hazards to acid (low pH) waters, while As remains mobile across a wider pH range.

mg/l Cu As

300 10

30 1

As 0 cu a

3 1 R O N DUKE

1 DIZON

a SHAMVA

0 PHILEX

a

GLOBE

0 RONPHIBUN @

LUCK^ HILL I O I I ! I I 1

I

0 PH

3: The hydrochemical data collated for some 50 sites portray a recurrent relationship between deposit geology (ore mineralogy, geochemistry and host-rock lithology) and post-mining effluent composition (Fig. 12). While the toxic trace element budgets of mine-waters are indisputably influenced by 'external' factors (such as climate and the extractive/mineral processing methods applied), the strength of this relationship indicates that inherent or 'internal' geological variables constitute the first-order environmental controls. The ability to predict the composition and magnitude of sydpost-extractive contamination in tropical regions from a knowledge of the empirical relationships outlined in Figure 12 could prove of enormous value for environmental impact assessments of future mining ventures. Furthermore, the available data indicate that predictive modelling of mine discharges, based on geological input parameters, is quite plausible.

17

Figure 12: Relationship between deposit geology and drainage chemistrj (pH and metal content), based on empirical data collected in for approximately 50 mines in Malaysia, Zimbabwe and the Philippines (abbreviations - A.S = acid sulphate. VMS = volcanogenic massive sulphide).

As (t Ni + Cu + CO + Zn)

( m g l ) 1000 A. s. EPITHERMA~

1 oc

OMPLEX SULPHIDE

10

1

SULPHIDE CONTENT .I

.01

1 2 3 4 5 6 7 8 9

6.1.3: Contaminant transport and fates. Field monitoring and mapping of the aqueous concentration and spatial distribution of As and heavy metals in metalliferous mining areas can provide valuable information regarding the extent of contaminant dispersal, but affords only a limited insight into the actual processes of contaminant transport and the mechanisms of deposition or attenuation. Using a combination of empirical, experimental and simulative (computer modelling) approaches, it has been possible to identify several different contaminant transport-attenuation systems at the project study sites, each of which would require ;I specific approach to pollutant mitigation or site remediation. The scenarios encountcred can be summarised a follows:-

1 : pH-mediared, hydrous Fe-oxidr . ~y . r t~~ms : At many of the gold and complex-sulphide mine sites investigated, AMD (pH <4) emanating from sulphidic waste dumps and adits was found to he characteristically enriched with Fe (sec Table 4), the solubility of which is strongly pH- dependent. With progressive downstream buffering (through water-rock interaction, or through dilution by less acid or alkaline tributary inputs), such mine-waters typically become 'saturated', with resultant prccipitation of Fe in one or more solid mineral phases. The most common minerals to precipitate are hydrous oxides (for example, goethite. fcrrihydrite) and are often conspicuous by their tendency to form an orange/yellow 'ochre' horizon on the affected stream bed (Fig. 13).

18

The ability of hydrous oxides to scavenge trace elements (notably As, Ba and first-row transition metals) from solution by processes of surface adsorption and co-precipitation is well known (for details see technical report WC/93/09/R). The simultaneous loss of Fe and several (otherwise undersaturated) elements (including As) from solution downstream of several mines in Malaysia, Zimbabwe and the Philippines (e.g. Fig. 14), coupled with analytical data showing acute As and heavy metal enrichment in ochrous sediments. has confirmed that this process constitutes an important natural mechanism of mine-water decontamination.

200 - 100 -

Figure 14: Variation of Fe, Cu, Zn and Ni in drainage downstream of a sulphidic waste- rock dump (and associated open-pit Cu-Au porphyry mining operation), Sabah, East Malaysia. A coincident loss of Fe and trace metals occurs through pH-induced Fe oxide precipitation (and subsequent scavenging) downstream of site M36 (illustrated in Fig. 13 B). All metal concentrations are given in mg/l. The horizontal axis relates to a downstream distance of 7 km.

- c u r 80

__t_ -60 - 40

- 20 - A = -

-

400 - 20

300 - 200 - - 10

100 - - Ni

0 . r . o

Laboratory leaching experiments conducted by BGS gcochemists have confirmed that As and heavy metals in the hydrous Fe oxide fraction of drainage sediments are strongly bound, and are relatively 'inert' in ecotoxicological terms. The ochre horizons observed in drainage sediments can thus be viewed as 'sinks' for metals and their induced precipitation, under carefully controlled circumstances, offers enormous potential for pollution mitigation.

2: pH-mediated, sulphate-domznured systems: The precipitation of Fe in sulphate mineral phases (notably melanterite and a variety of jarosites), with concomitant removal of As and heavy metals, has occasionally been observed in mine-waters in Zimbabwe and the Philippines with extremely high concentrations of dissolved SO4 (Fig. 15). The process

20

Fig 17: Total As, arsenate and Eh profiles in surface drainage at Lucky Hill mine, near Bau, Sarawak. A depression of Eh at the site of the mine induces a corresponding increase in As solubility. A coincident fall in the percentage of total As present as arsenate, confirms that the enrichment occurs mainly in the form of arsenite.

100 7

10 7

1 .

m Y

- Eh - As

L. % As(V) Mine working

I 1 1 I 1 I 1

4: Systems mediated by o r ~ ' m i c coniplr.riri~ ( i ~ o i i t s : The use of organic complexing agents, notably cyanide (CN) compounds, for recovering gold from non-refractory ores is widespread throughout the developing world (for process details see technical report WC/94/65/R), and the presence of CN- compounds in drainage emanating from heap-leach operations and tailings impoundments has been detected at several project study sites. While of no direct environmental concern (due to their rapid breakdown to harmless compounds), the aqueous stability and degradation of CN- complexes has been found to exert a first-order control on toxic trace element mobility under high pH conditions which would otherwise inhibit metal solubility.

A spectacular example of the impact of cyanide on toxic trace element transport in mine- waters was recorded at the Globe and Phoenix mine, Kwekwe, Zimbabwe. During low- rainfall periods, the dominant component of total discharge in drainage to the west of the tailings impoundment at this site was found to be derived from alkaline mine-process waters. At the time of sampling in 1994, residual cyanide in the upper reaches of this discharge was sufficient to retain Fe. Cu. Zn, CO and Ni in solution (at concentrations of up to 50 times international potable water limits) through the formation of cyanic complexes. The metalloids. As and Sb, were also found to be enriched by 2-3 orders of magnitude (Fig. 18). In this particular instance, the toxic hazard was short-lived, as 3 downstream rcduction of pH (to 4, following the introduction of acidic drainage from sulphide waste piles) induced the breakdown of the organo-metallic complexes, Lrolutisution o i cyanide and precipitation of

2 3

metals (within the confines ol' the mining concession area). Under circumstances which favour the persistence of strongly alkaline waters over greater distances, the dispersal of toxic trace elements in cyanic complexes could, however, prove more problematic and might constitute an' environmental hazard.

Figure 18: pH and dissolved trace element profiles in drainage waters from the Globe and Phoenix tailings impoundment, Kwekwe, Zimbabwe. High toxic element solubility is retained at high pH levels in the upper reaches of the system due to complexation with cyanide. Precipitation of metals occurs in the downstream environment due to the reduction of pH (to ~ 8 . 0 ) and the attendant breakdown of metal-cyanide complexes. All trace element values are shown in pgh. The horizontal axis represents a distance of c. 3 km.

Log metals (pg/l) 100000

10000 - Ni 1000 - C O

- c u 100 10

1 .1

.01 .Do1

GPW 110 GPW 108 GPW 101 GPW 102 GPW 103 GPW 104

I ' 1 1 I I I I

GPW 110 GPW 108 GPW 101 GPW102 GPW 103 GPW 104

6.1.4: Geochemical modellinr.: Throughout the project, empirical and cxpcrimental studies of the concentration and geochemical form of As and toxic metals in mine-waters have been supplemented by simulative modelling of processes. using commercially available thermodynamic codes such as WATEQ4F, PHREEQE and LIINTEQ. This approach (dcscribed in detail in technical reports WC/94/09/R, WC/94/7X/R and WC/94/79/R) has proved of particular value for (,i) determining the dominant dissolved species ol' As and heavy metals in mine-waters, (ii) predicting the locations in which these elements may become saturated (and thc chemical form of precipitation products), and ( i i i ) assessing the likely effectiveness o f pollution mitigation strategies such as liming.

24

The chemical speciation of As in mine-water has a critical bearing on both it's mobility and toxicity. Although certain species can be determined analytically, the ability to predict the probable form of As in any given aquatic system using thermodynamic equilibria can preclude the need for costly analytical hardware. An example of the contrasting modelled speciation of As in surface drainage, shallow groundwater and deep aquifer waters from the As-contaminated district of Ron Phibun, southern Thailand, is provided in Figure 19. Although the highest total concentrations of As at this site occur in shallow groundwaters, the most toxic form (arsenite, H3As03) is most prevalent in the deep aquifer. Modelled output of this nature has considerable applicability in human risk assessment studies, allowing total concentration data to be normalised against species-controlled toxicity variations.

Figure 19: Modelled speciation of As in surface drainage, shallow groundwater and deep aquifer water: Ron Phibun, southern Thailand.

Deep groundwater (reducing, pH 7) Shallow groundwater (pH6) Surfaco water (pH3)

The utility of geochemical modelling as a tool for predicting the effects of mine-water management strategies such as liming was evaluated for the Mamut Cu-Au operation in Sabah and the Iron Duke mine in Zimbabwe (technical reports WC/94/09/R and WC/94/78/Rl. At Iron Duke, a simulative exercise involving the neutralisation of mine-water with a pH of <1.0 and holding zxtremely high toxic trace element concentrations (for example, 70 mg/l A s , 20 mg/1 Cr, 50 mg/l Zn) was conducted to determine the amount of lime required. the effect on contaminant solubility and the chemical form of precipitation products. Results were highly encouraging, indicating that Fe oxyhydroxide precipitation could be instigated, with trace metals precipitated 3s a range of sulphates and hydrous oxides.

25

On the basis of these modelled predictions, field trials of liming-based pollution mitigation methods were deemed appropriate.

6.1.5: Soil studies: Gold and complex-sulphide orebodies characteristically produce localised enrichment of As and heavy metals in the overburden through natural weathering mechanisms. The controls on the geochemistry of these soil 'halos' have been widely studied by exploration geochemists. However, the mobility, geochemistry and toxicity of As and toxic heavy metals in the DOS^- mining tropical soil environment remains to be fully appraised.

I

Investigations (involving geochemical, mineralogical and grandometric methods) of soil As contamination were undertaken at the Penjom gold mine and Mengapur complex-sulphide prospect (technical reports WC/94/20/R and WC/94/26/R), Peninsular Malaysia, and within RTZ and Tabex mining concessions in the Battlefields and Kwekwe areas of the Midlands greenstone belt, Zimbabwe (technical reports WC/94/50/R and WC/94/65/R). The principal findings are summarised below:-

1: Comparative studies of the concentration and lateral distribution of A s along geologically and lithologically comparable transects ( 1-2 km in length) bisecting mineralised structures have confirmed that significant soil As enrichment, over and above the natural mineralised background, can occur as a consequence of overburden disturbance. For example, sub-surface (B horizon) soil concentrations of 800-1800 pg/g were recorded in parts of the Penjom mine area which had been subject to extensive open-pit gold extraction. Values of 200-400 pg/g

were established as typical of the 'natural' mineralisation halo in the area (Fig. 20).

Figure 20: Lateral distribution of As in soil transects bisecting mined and unmined sectors of a gold-bearing shear zone at Penjom, Peninsular Malaysia, showing significant relative enhancement in an area of mining disturbance.

1000

800

600

As P9/9 500

400

200

0 9 0 ' 9 0 2 c 0 3 0 0 8 8 0 0 9000 9200 9400 9600 9800 10000 ' 0 2 0 0

- E3Sbflg :3Ssring

26

Figure 23: Selective extraction scheme for the determination of particulate As species in soil and sediments.

\A ~ dryweight

haka fw 1 hr with i \

i", U Ammonium iLould

I f

Shake for 1 hr.

oxides

1 Solid

I

1 I Mix with Tamm's ' Aeagent and allowi Liquid

1 Perform hm acid attack on solid residue.

Figure 24: Soii partitioning of As in 'B' and 'C' horizon samples from a mineralised soil profile at Penjom, Malaysia. In the basal C horizon (near the soil-bedrock interface), As is predominantly held in residual phases (e.g. detrital sulphides) derived from the partially weathered bedrock. In the more intensely weathered B horizon, the residual As-carriers break down, but the As released is rapidly immobilised in ferric oxide phases, which show increased overall importance.

8.82% 7.35% 6.45%

8 87% Aasorbed

'-UIVIC

riurnic

M n-oxide 4 03%

u c - h or i zo n

4 1 ,94%

29

4: Mineralogical studies and laboratory leaching experiments of As-contaminated soils from Zimbabwe and southern Thailand have shown that As can be highly mobile in soils with very low (4%) Fe content. In Fe-poor carbonate soils, there is a tendency for soluble calcium- arsenate (rather than insoluble ferric-arsenate) mineral phases to form following the liberation of As from primary detrital minerals. In some alluvial soils (such as prevail to the north of the Globe and Phoenix waste dumps at Kwekwe, Zimbabwe), the absence of either organic or femc oxide scavengers has been shown to result in the formation of highly-soluble As oxide coatings on soil particles. These c m be tlushed into drainage/groundwaters or be uptaken in solution by plant roots, posing a clear human and ecotoxicological hazard.

5: In undisturbed soils, the vertical distribution ol' As varies significantly with soil maturity. In relatively immature, poorly-zoned Malaysian soils, As concentrations are typically highest at the soilhedrock interface and decline progressively upward towards the rooting zone. In contrast, more ancient, intensely weathered profiles (typical of African soils) show marked enrichment of As in mid-profile, usually in association with a well-defined Fe-A1 oxide horizon.

6: Data for the Battlefields and Kwekwc areas of Zimbabwe. and from southern Thailand suggest that As concentrations in surfacdmid-profile soils arc systematically reduced as a result of agricultural ploughing and furrowing. An example from the vicinity of the Globe and Phoenix mine, Kwekwe, is provided in Fig 25, in which As and selected heavy metal concentrations are plotted along an east-west trending transect.

Figure 25: Concentration (pdg) of As and selected heavy metals in 'B' horizon soils along an E-W trending transect at the margin of the Globe and Phoenix concession area, Kwekwe, Zimbabwe.

loo00 - As - Sb - w

100 j

10 7

ICQ I 1

1 . 1 1 I 1 T 1 1

P - Pb e

GPSl GPS2 GPS6 GPS7 GPSB GPSS GPSlO G P S l l GPS12

30

High As levels (typical of the local terrain) are recorded in undisturbed soils at the western extremity of the transect, but decline abruptly on entering a ploughed area (planted with maize) to the east of site GPS2. The phenomenon could be attributable to either (i) increased physical downwash of heavy minerals (including detrital sulphides) and clays in response to increased soil infiltration and permeability, or (ii) increased oxidation and dissolution of detrital sulphides, caused by soil aeration. Should the latter process prove dominant, the net effect could be to increase As mobility and bioavailability, with important implications for crop assimilation.

6: Granulometric analyses of As-enriched soils from Malaysia and Zimbabwe have confirmed that disproportionate enrichment occurs in ultrafine fractions with a particle size of <20 pm. These ultrafine phases comprise clays (with high specific adsorption surfaces) and discrete ferric oxide particles which are readily outwashed from the soil following devegetation or other mining-related physical disturbance. Although sediment traps are frequently used in the mining industry to restrict the adverse impacts of physical siltation, these highly- contaminated particulates can remain suspended at very low flow velocities, and are thus not effectively entrained. Problems of outwash from contaminated soil are particularly acute in tropical mining regions, due to the typically high intensities of rainfall. The implementation of technology for the removal of ultrafine particulate contaminants (for example, flocculation methods) from surface drainage waters is thus particularly required in such settings.

6.1.6: Bioassimilation studies: Data showing the abundance and geochemical form (including theoretical bioavailability) of mine-derived contaminants in water or soil can provide a direct insight into the potential human and ecotoxicological hazard. Supplementary information showing the actual extent of toxic trace element uptake into biota and translocation through food chains is, however, valuable for more qualified risk assessments, and the evaluation of site remediation requirements.

Arsenic and heavy metal bioassays were conducted by ITE and NHM staff (in close liaison with BGS geochemists) at selected project study sites in Malaysia and Zimbabwe. These field investigations fell into discrete 'aquatic' and 'terrcstrial' units, the former conducted primarily at Malaysian sites and the latter mainly in Zimbabwe.

Preliminary aquatic bioassimilation studies at Penjom and Mengapur, Peninsular Malaysia (described in detail in an ITE technical report, Cummins and Wyatt, 1994) entailed the collection of flora and fauna from over 40 watcrcourses and flooded alluvial gold workings. The ability of algae to concentrate As is well documented, and at Penjom several filamentous algae samples yielded As concentrations 2-4 orders of magnitude higher than those in the

31

In the terrestrial environment, invertebrates (notably earthworms and nematodes) were selected as the primary sample media for assessing As and heavy metal bioassimilation. Earthworms are important with respect to a range of soil-forming and nutrient-cycling processes and form the basal level of many complex food chains. They are also virtually ubiquitous, and thus provide a good basis for inter-site data comparisons.

In 1994, samples from the Globe and Phoenix, Wanderer, Iron Duke and Shamva mines in Zimbabwe were collected and analysed for As by ITE. The results showed marked As

enrichment in body tissues (to several thousand pg/g) in areas of mining disturbance, and confirmed a direct relationship between As body burdens and ambient soil concentrations. It should be emphasised that the soil As distribution at all sites is, to a large extent, inherently controlled by natural bedrock mineralisation. However, the invertebrate data demonstrate that any magnification of soil As loadings, for example, through the deposition of tailings, can induce a corresponding increase in fauna1 bioassimilation. Efforts by ITE towards improved methods of data interpretation, including body-weight normalisation and compensation for As held in detrital 'gut' material (both significant problems in previous studies) should prove of value for future researchers conducting invertebrate bioassimilation assays.

Terrestrial vegetation samples from several mine sites in Zimbabwe were collected during a field excursion in 1994. Emphasis was placed on the analysis of subsistencdcash agricultural crops which may directly influence human dietary As exposure. The results highlighted marked between-site variations in the level of As uptake for important species, notably maize (Table 7). In the Battlefields area of Zimbabwe, relatively low As values ( c l pg/g dry weight) were systematically recorded in both maize and natural grasses growing close to several small gold mines, in soils containing >1000 pg/g As. While a concentration of 1 pg/g in grasses is 1-2 orders of magnitude above the 'global average', no real toxicological threat is posed, and the ratio of As in vegetatiodsoil is remarkably low. In contrast, maize cobs, leaves and roots containing over 10 pg/g dry weight As (also enriched in antimony) were recorded from floodplain soils (1OO0-5OOO pg/g total As content) near the Globe and Phoenix mine, Kwekwe. Such concentrations in staple crops will inevitably result in a high As exposure within the local population, the long-term medical consequences of which warrants urgent attention.

High levels of plant uptake appear to occur almost exclusively in areas of low (4%) soil iron content (typically alluvial soils). This problem may be further exacerbated by very low (<0. 1%) soil phosphorus levels, as As provides a close geochemical analogue with resultant root uptake by substitution. In tropical soils with moderate or high soil Fe contents (10-3O%)

these detrimental assimilation processes are impeded by the chemical hinding/immobilising effect of ferric oxides on As (and several heavy metals).

33

6.1.7: Ecotoxicological m o n i t o r i s Methods for assessing the toxicological impacts of trace element contamination are fundamental to any comprehensive mining-related environmental monitoring programme. There remains, however, a severe lack of low-cost ecotoxicological field methods, suitable for systematic use in tropical developing countries. As a consequence, the collation of data regarding the biological and human impact of As and heavy metals mobilised by mining activities in tropical environments has, hitherto, been impeded.

At the project outset, the development of a simple technique for detecting early-stage ecotoxicological effects of As contamination was identified as a central research priority. Cellular (or sub-cellular) responses to pollutants can, in theory, provide particularly sensitive indicators of toxic-stress, and a microscopic 'biomarker' approach was, therefore, favoured. A pioneering field method was developed by ITE utilising a molecular probe, formerly devised for use with marine organisms (for full details see technical report WC/94/66/R). The technique entailed the extraction of coelomic fluid from invertebrate samples using an ultrafine hypodermic needle. The fluid from each sample was then transferred into an isotonic ringer, loaded with neutral red dye and observed under an optical microscope at 10 minute intervals. Because the ability of cells to uptake and retain the dye in the lysosomal compartment is directly related to cell health, temporal dye-loss trends provide a direct indication of cell dysfunction.

The neutral-red assay method was pilot- tested along a known As contamination gradient (previously defined by soil and stream sediment analysis) extending some 6 km downstream of the Wanderer mine dump, near Shurugwi, Zimbabwe (technical report WC/94/66/R, Fig. 5). A single, locally ubiquitous earthworm species (Amynthas gracilis) was used as a biomarker source. In accordance with expectations, cells extracted from earthworms collected in close proximity to the dump (i.e.. in areas of highest As exposure) showed rapid leakage of the neutral-red dye (within 5 minutes) from the lysosomal compartment into the cytoplasm, indicating extensive toxic membrane damage. Dye retention times showed a significant increase with increasing distance from the spoil site. Analyses of earthworm body-burdens confirmed an inverse correlation between As exposure and lysosomal dye retention time (Fig. 28). Subsequent laboratory experiments demonstrated beyond doubt that the behavioural variations observed between 'healthy' and 'stressed' cells at Wanderer could be ascribed almost entirely to differences of As assimilation.

Although additional field tests are required, the neutral-red assay field trial conducted at Wanderer mine has highlighted the considerable potential of this new, cost-effective in vitro biomarker technique for the assessment of biological impacts of mining-related As contamination world-wide. With appropriate caution, the method should be equally

35

applicable for assessing impacts of multiple-element exposures, including metalloid-heavy metal 'cocktails'.

Figure 28: Relationship between As body-burden in earthworms and lysosomal retention of neutral-red dye (minutes) for samples collected at varying distances from the Wanderer gold mine, Zimbabwe.

e NRR TIME (Mind

0 EARTHWORM As CONTENT (pg) 200

Comparative studies of aquatic faunal/kloral diversity at 'pristine' and 'disturbed' mining localities in Malaysia were undertaken by NHM staff in 1994. Preliminary results (described in an NHM technical report, Bowel1 et al., 1994) confirmed the utility of ciliates and nematodes as indicators of mining-induced toxic stress. Severe ecological dysfunction at some sampling sites at Jugan, near Bau, Sarawak (a gold mining locality with up to 4 ms/l As in surface waters) was signified by the virtual absence of a nematode community and associated anomalies in the ciliate community structure.

6.2: Hazard mitigation and site remediation options

A review of mine-water treatment and site remediation methods currently deployed in Europe and North America was undertaken at the project outset with the aim of identifying technologies which, with suitable modification, could be utilised in tropical developing countries. The principal criteria used to dcfine suitability were (i) the cost and availability of raw materials, (ii) the technological expertise required for implementation, (iii) the extent and cost of post-implementation maintenance, (iv) mcthod versatility.

36

Buffering methods, including liming and limestone drain implementation, although technically simple were found to have potential shortcomings with respect to several project study sites due to a failure to effectively remove As (particularly in waters with low dissolved Fe concentrations). Free-liming has additional limitations as a post-closure site remediation option, due to the perpetual requirement for human involvement. At numerous sites, for example Mamut in central Sabah, no local source of lime could be identified for long-term use, and long distance transportation was considered to critically affect the cost-benefit equation.

Recent project investigations have focused on two highly versatile approaches with practical applicability in virtually all tropical developing countries:-

1: Wetland systems (Figure 29) which act to remove toxic elements from mine-waters by particulate sedimentation, sulphide precipitation, hydrous oxide formation, organo-metallic complexation and cation-exchange processes. The approach has shown considerable potential at several project study sites in Zimbabwe and Malaysia, and is particularly appropriate in localities where a high proportion of the contaminant load is transported as particulate outwash, or where As (which is effectively sorbed and complcxcd by the organic matrix) is a primary contaminant.

2: Waste-water treatment involving the sorption and subsequent recovery of As and heavy metals using scavenging properties of hydrous ferric oxides (HFO) has been investigated using a combination of experimental and simulative methods. The HFO can generally be precipitated using dissolved Fe which is naturally present in the mine-water, but can also be introduced to the discharge (or substituted by resins) in Fe-poor waters. A combined saturation-speciation and two-layer sorp lion model (GTLM), developed specifically for testing the applicability of the method in individual mine-water settings, has confirmed that As tends to be recovered with remarkable efficiency. The model functions by calculating (i) the percentage of dissolved Fe which will precipitate as HFO under a specified pWEh regime and then (ii) the co-ordination sites available for contaminant sorption on the precipitated oxide surfaces and (iii) the rclative rates of dissolved trace element sorption. An example of the use of the model for predicting the effectiveness of induced ferric oxide precipitation for decontaminating waste-water at Mamut mine, Sabah, is shown in Figure 30. Input data for a headwater area near the West Dump at the site, containing 310 mg/l dissolved Fe, >100 mg/l Zn and >250 mg/l Cu, 1 mg/l Pb and 0.5 m d l As (at pH ~ 3 . 0 ) were used as model inputs. Assuming 100% precipitation of dissolved Fe as HFO, the scavenging effects on selected trace metals are modelled at various pH levels. Arsenic is scavenged effectively under a wide

37

range of pH conditions, while significant recovery of' elements such as Pb (>60%) and Cu

(40%) occurs only at a higher pH (8.0).

AIR

0 0 o v 0 WATER

0 2: OXIDATION ANDA

Figure 29: Principles of wetland remediation systems.

SOIL 5: ORGANO-METALLIC PRECIPITATION

(HYDROUS OXID COMPLEXATION

Figure 30: Generalised two layer sorption modelling for selected trace metals in drainage waters from Mamut mine, Sabah, following the precipitation of 100% of the Fe loading (310 mgA) as hydrous ferric oxide. The recovery profiles indicate that induced precipitation of Fe in such waters can provide a cheap, convenient method of removing contaminants such as As, without necessarily neutralising the AMD.

YO sorption 100 80 60 40 20 0

2 3 4 5 6 7 8 PH

38

'Natural analogue' decontamination systems were ohscrved at several study sites. For example, at Jugan, Sarawak, As-rich waters showed evidence of purification following percolation through a sand and gravel matrix of outwash detritus, derived from the mined area. Trials have been proposed (report WC/94/67/R) to assess the wider utility of such gravel beds for treating As-rich stream waters, with a view to developing a low-cost amelioration system for use at Jugan and similar settings elsewhere.

At certain study localities, human regulation of mine drainage quality appeared warranted only on an intermittent basis, to mitigate the effects of short-lived pollutant 'pulses' or brief poor water quality episodes. At Mamut, Sabah, drainage quality in the Sungai Liwagu system to the south of the mine was found to decline (with enhanced Cu, A1 and Fe loadings) specifically during peak discharge events as a consequence of the temporarily increased contribution to total streamflow derived from a hydrologically 'flashy' mine-impacted sub- catchment area. This short-term water quality hazard was shown to be avoidable by partial impoundment of drainage in this sub-catchment in such a manner that it could contribute no more than 25% of total basin discharge during storm events, and a full-scale pilot study was discussed with the site operators in 1993 (technical report WC/94/09/R).

6.3: Predictive modelling and environmental impact assessment

Geochemical monitoring methods, while suitable for short-medium term assessments of the distribution, chemical form and toxicity of mine-derived pollutants, do not facilitate estimations of long-term (10-103 yr) contaminant iluxes from adits or waste dumps of the nature required for reliable cost-benefit analyses of site remediation options. A simulative model, capable of predicting long-term mine drainage quality could be invaluable for this purpose. With increasingly stringent environmental legislation now being imposed on the minerals sector worldwide, pollution control costs can significantly influence deposit viability. A model with the capacity to predict contaminant tluxes and likely mitigation requirements at hitherto unexploitcd deposits could therefore prove of additional value to minerals economists. Mine drainage modelling offers particular benefits in tropical developing countries which have an acute lack of human and capital resources for empirical monitoring and analysis. In regions with limited funds for site remediation, a versatile mine effluent model could also play a role in identifying areas of greatest long-term environmental risk.

Although the controls on mine drainage chemistry arc complex, BGS data for over 50 mines in a diversity of geological and metallogcnic settings suggest that a small number of 'first order' influences are operative at all sites (see section 6.1.2). The incorporation of theoretical and empirical data for these components within a relational database offers potential for semi-

39

quantitative predictive modelling of drainage outputs. Thc approach is particularly applicable to relatively homogenous contaminant sources (e.g. tailings piles), but has additional potential for more complex waste rock dumps, open pit and adit settings.

A provisional model framework has been devcloped by BGS, which can utilise empirical andor estimated input data for deposit mineralogy, chemistry, hydrology and engineering properties in the modelling process (Fig. 3 1 ) .

Figure 31: Conceptual BGS model for the prediction of mine drainage quality: ( i ) calculation of net-drainage acidity from mineralogical and hydrogeological variables, (ii) calculation of gross metal loadings through thermodynamic and surface-reaction modelling of contaminated waters during transport through the waste/adit environment. WRI = water rock intcraciion indcx.

PREDICTNE MODELLING OF MINE DRAINACE QUALITY: 1:

Fluid flow ditsoM4, rmlphidc mincralOgY, charadcntia mioaalogydgranulamby wcatbcringmdim

PCnmabilityBt wR&Auinautphidc Host & gangue * DATA MANAGEMENT &

WRI INDEX

'ERROGATION SYSTEM

.1 SULPHIDE OXIDATION

RATE AT WATER-ROCK B

NET DRAINAGE ACIDITY

PREDICTIVE MODELLING OF MINE DRAINAGE QUALITY: 2:

SULPHIDE OXIDATION RATE AT WATER-ROCX I N S I W

WINDEX INTERFACE BUFFERING

DRAINAGE VOLUME, pH AND MOBILISED (GTLM FOR

+ METAL BUDGET

( W A T E Q m Q + CODE $:gzzU SATURATION- SPECIATION

MASS TRANSFER DATA + OUTFLOW METAL LOADING

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For any given site 'net drainage acidity' can be calculated as a function of water-rock interaction (WRI), flow-indices, gross sulphide oxidation and gangue/host rock buffering. Dissolved metal loadings can then be predicted from mineralogical data, modified thermodynamic codes (based on MINTEQ) and sorption indices.

A future BGS priority is the design of a Knowledge-Based Expert System (KBES) to encapsulate the model codes, software, and empirical database. This approach is potentially valuable for assisting in prediction and providing decision-support in many areas where model uncertainty andor partial data exist, and human expertise is a major requirement of the problem-solving process. The KBES allows different contamination and site management scenarios to be compared by intelligent control of model parameters, coupled with automated reasoning processes. Additional software has rcccntly been developed by BGS to encompass the KBES within a broader Geographic Information System (GIS) framework, thus facilitating full spatial modelling of contaminant transport.

7: RESEARCH TAKE-UP

Attempts were made to promote the practical take-up of research findings by public and private sector collaborators throughout the study. Areas in which this policy has proved potentially successful include:-

1: Thailand: In 1994, the Department of Mineral Resources allocated 5 million Baht for decontamination of As-rich water supplies at Ron Phibun. Data collected for the site by BGS are being used in the design of an appropriate pollution mitigation strategy. A request for continued BGS involvement in the remediation programme was submitted to ODA in September 1994.

2: Philippines: The Mines and Geosciences Bureau are currently revising national environmental legislation relating to the small-scale mining sector. BGS data could provide a framework for the identification of practical guidelines/thresholds for environmental contaminants which account for (i) the naturally anomalous concentrations of elements such as As in gold mining areas and (ii) the limited technological support currently available to small-scale operators.

3: Malaysia: The Geological Survey of Malaysia and commercial operators are currently utilising several of the BGS monitoring and data interpretation procedures developed during the project. Pilot-testing of BGS remediation options at selected sites was planned during 1993, but subsequently deferred due to short-term political sensitivities.

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8: CONCLUSIONS

The research conducted under BGS/ODA TDR programme 92/6 (ref. 5553) has provided a basic framework for monitoring, predicting and mitigating mining-related As and heavy metal contaminant hazards in tropical developing regions. The general conclusions to be drawn from the work outlined in this report, and in the preceding series of site-specific technical reports (Appendix l), can be summarised as follows:-

1: The magnitude and extent of As and heavy metal contamination associated with gold and complex sulphide mining is highly variable, but is a predictable function of geological and technological factors. By clarifying a range of 'first order' controls, it has proved possible to develop an empirical basis for rapidly identifying sites where severe problems may occur, and where remediation efforts are most warranted.

2: Mineralogical and geochemical characterisation of 'contaminant sources' (for example, waste piles, adit exposures), although largely neglected in mine-water investigations, has been confirmed as a valuable mechanism for assessing potential risk. The role of 'environmental mineralogy' in mine-contaminant studies has thus been firmly established.

3: The processes of metal transport and attenuation in mine waters are non-uniform. Their characterisation, using techniques and classifications such as outlined in this study, is a vital prerequisite for successful risk assessment and mitigation system design.

4: Bioassimilation of As and heavy metals is subject to marked spatial variability. The range of simple pedogeochemical and ecotoxicological methods developed by BGS and ITE should find widespread application in future assessments of the biological impacts of mine- derived contaminants (in the targeted study areas and elsewhere in the tropics).

5: The toxicology of As and heavy metals liberated by gold and complex sulphide mining is determined by both concentration and speciation. The geochemical modelling and analytical speciation methods developed during this study should provide a valuable protocol for future monitoring programmes.

6: The 'buffering' methods conventionally used to treat acid mine-waters are inadequate for universal use in mitigating As contamination. The range of alternative methods outlined in this study, including bio-remediation and pH-independent chemical scavenging systems, should provide superior results in tropical developing countries.

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7: The highly variable degree of practical 'take-up' (to date) of research findings in the localities visited during this TDR programme is rellective, in part, of the regionally differing levels of publicflegislative pressure for improved environmental control on the mining sector. This trend has served to emphasise the need to complement international technical support (of the nature provided by the ODA) with domestic legislative pressure to promote or enforce environmental protection.

8: Practical take-up of the findings of this research will also inevitably depend on the availability of appropriately trained government-sector personnel (and capital resources) to undertake continuous monitoring and legislative enforcement. The possibility of longer-term training, through Technical Co-operation or analogous programmes could warrant consideration.

9: ACKNOWLEDGEMENTS:

Permission to undertake research in Malaysia, the Philippines, Zimbabwe and Thailand was kindly granted by Mr Fateh Chand (Director General, Geological Survey of Malaysia), Mr Joel D Muyco (Director, Mines and Geosciences Bureau, Philippines), Dr John Orpen (former Director, Zimbabwe Geological Survey Department) and Dr Pricha Attavipach (Director, Department of Mineral Resources, Thailand). Sincere thanks are extended to the staff of each of these departments for the provision of local expertise, field personnel, vehicles and related logistic support during field visits. Valuable support and guidance was also provided by resident BGS -0DA TC oflicers in Malaysia (Mr A G Gunn) and Zimbabwe (Dr P Pitfield and Dr P Lowenstein). The British High Commission, Harare, generously provided a vehicle for use throughout the 1993 and 1994 field campaigns in Zimbabwe.

Permission to sample within current mining or exploration concessions in Malaysia, the Philippines, Zimbabwe and Thailand was provided by Luckfrost UK, Malaysia Mining Corporation, Mamut Copper Mining, Bukit Young Mining, Leadstar Mining, Philex Mines, Benguet Corp., Dizon Mines, Rio Tinto (Zimbabwe), Lonrho, Tabex Mining, Union Carbide and Anglo American Corp.

Support and guidance relating to field activities in Asia and southern Africa was provided by BGS Regional Geologists, Mr R B Evans (Asia), Dr R L Johnson and Mr A MacFarlane (Africa).

4 3

APPENDIX 1: PROJECT TECHNICAL REPORTS

Williams, T.M., Breward, N., Gunn, A.G. and Cummins, C. 1993: Environmental geochemistry of the Penjom Mine area, Kuala Lipis, Pahang, Malaysia: Preliminary results with particular reference to arsenic. British Geological Survey Overseas Geology Series Technical Reprt WC/94/20R.

Williams, T.M., Breward, N and Smith, B. 1994: Environmental geochemistry of the Mamut copper mine, Sabah, East Malaysia. British Geological Survey Overseas Geology Series Technical Report WC/94/9R.

Breward, N., Williams, T.M. and Cummins, C. 1994: Environmental Geochemistry of the Mengapur and Sungai Luit mining areas, near Kuantan, Pahang, Malaysia. British Geological Survey, Overseas Geology Series, Technical Report WC/94/26?R.

Breward, N and Williams, T.M: 1994: Environmental geochemistry of the Bau area, Sarawak, East Malaysia. British Geological Survey Overseas Geology Series Technical Report, WC/94/67/R.

Williams, T.M. and Smith, B. 1994: Supergene geocheniistry of arsenic, antimony and associated elements a t Globe and Phoenix Mine, Kwekwe, Zimbabwe. British Geological Survey Overseas Geology Series Technical Report, WC/94/65/R.

Weeks, J. and Williams, T.M : 1994: Preliminary field trial of a method for the rapid assessment of invertebrate stress from mining-related gold and heavy metal contamination. Wanderer gold mine, Zimbabwe. British Geological Survey Overseas Geology Series Technical Report, WC/94/66/R.

Naden, J., and Bland, D.J: 1994: Mineralogical studies of Au-As-Sb mineralisation, mine wastes and soils in the Kwekwe area, Zimbabwe. British Geological Survey Overseas Geology Series Technical Report, WC/94/50/R.

Williams T M and Smith, B 1994: Empirical and modelled hydrochemistry of acid mine drainage, Iron Duke mine, Mazowe, Zimbabwe. British Geological Survey Overseas Geology Series Technical Report, wc/94/ 18rR.

Fordyce, F.M, Williams, T.M, Paijitprapapon, A and Charoenchaisri, P. 1994: Hydro-geochemistry of arsenic in an area of chronic mining-related arsenbm: Ron I’hibun District, Sakhon Si Thammarat Province, Thailand. British Geological Survey Overseas Geology Series Technical Report WC/94/79/R.

Bowel1 R J: 1994: A review of mineralogical processes affecting sulphide minerals during tropical weathering. Natural History Museum technical report.

Douglas, G E., Brooks, S J., Hodda, D.M. and Warren, A: 1994: Micro-ecological aspects of mine contamination. Natural History Museum technical report.

Cummins, C and Wyatt, C L: 1994: Environmental geocheniistry of the Penjom and Mengapur mine areas: preliminary studies of arsenic and mercury in aquatic Iiiota. Inst. Terrestrial Ecology technical report.

Williams, T.M. 1995: Hydrochemistry of mine-waters associated with porphyry Cu-Au and epithermal gold mining operations, North Luzon, Philippines. British Geological Survey Overseas Geology Series Technical Report WC/95/15/R,

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APPENDIX 2: OTHER PROJECT PUBLICATIONS AND PRESENTATIONS

Williams, T.M., Breward, N., Lumb, A.J and Cummins, C. 1993: Trace element contamination around centres of gold mining: Examples from Peninsular Malaysia. Abstracts volume: SEGH, Aberystwyth, April, 1993.

Williams, T.M., Breward, N and Cummins, C. 1993: Arsenic contamination arsenic associated with gold mineralisation and mining in Malaysia. Proceedings of International Conference on Arsenic Exposure, New Orleans, 1993.

Williams, T.M. and Breward, N. 1993: Prediction and monitoring of acid mine drainage: Abstracts volume: Mineral Deposit Study Group, NHM, London.

Williams, T.M., Breward, N. Lumb, A., Cummins, C. and Jadid, M.B.M. 1993: Mobility and bioassimilation of arsenic associated with gold mineralisation and mining: examples from Malaysia and Zimbabwe. JAGID-SEGH conference on Environmental Geochemistry and Health in Developing Countries, London, October 1993.

Williams, T.M., Breward, N., Lumb, A.J and Cummins, C. 1994: Trace element contamination around centres of gold mining. Environmental Geochemistry xicl IIealtli, Vol 16, no 2., 90.

Breward, N, Williams, T.M. and Bradley, D: 1994: Comparison of alternative extraction methods for determining particulate metal speciation. SEGH, Krakow.

Williams, T.M. Geochemistry of waste dump drainage around a large Cu-Au porphyry operation. 12th European meeting of the Society of Geochemistry and Health, Keyworth, Nottingham, April, 1994.

Williams, T.M. 1994: Chemistry of acid mine drainage. Third international conference on trace metals in the aquatic environment. Aarhus, Denmark. May, 1994.

Breward N and Williams, T M: 1994: Arsenic and mercury pollution in gold mining: Mining Environmental Management. Dec. 1994,25-29.

Weeks, J. and Williams, T.M: A simple ecotoxicological field test to determine mining-related heavy toxic trace element stress. Science of the Total Environment (in press).

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APPENDIX 3: LOCAL DISSEMINATION

1993: SEMINAR, GSM, KUAIA I,UMPUK, MALAYSIA (PENJOM)

1993: ANALYTICAL METHODS 1'IIAINING, GSM, KUCHING, MALAYSIA

1994: SEMINAR, GSM, KOI'A KINABALLJ MALAYSIA (MAMUT)

1W4: SEMINAR SERIES, MGB, MANILA, 1'1 II1,IPPINES (PROJECT OVERVIEW)

FORMAL TRAINING

An MSc thesis, undertaken by Mior Sallehuddin bin Mior Jadid, a Geological Survey of Malaysia staff member on secondment to the University of Lancaster, was prepared using field data for Malaysian sites collected under BGS/ODA TDR project 92/6. The MSc research, entitled 'Geochemical Impact of Metal Mining activity at Penjom and Mengapur, Pahang, Malaysia', was supervised and examined by Dr T M Williams of the BGS. The thesis is held by the University of Lancaster under a 'rcstricted' classification, and provides a useful addition the BGS project technical reports.